Fire alarm



Dec. 28, 1954 A P. N. LEHR ET AL 2,698,368

FIRE ALARM Filed June 8, 1951 ff' /21 25:17-1 H3 1x i Mm-L /9 I7 L 23 2 tlz v T/5 ,8/ FIG. l

BY JOSEF K oc/ United States Patent O FIRE ALARM Philip N. Lehr7 Huntington, and Josef Koei, Jackson Heights, N. Y., assignors to Dictograph Products Company, Inc., Jamaica, N. Y., a corporation of Delaware Application June 8, 1951, Serial No. 230,576 6 Claims. (Cl. 20D-138) This invention relates to fire alarm apparatus, and has particular reference to fire detecting apparatus which is selectively responsive to an unusually rapid rise in temperature and an excessively high temperature.

Various types of fire detecting apparatus are in current use which respond thermostatically, photoelectrically, both thermostatically and photoelectrically, or by fusion of a low melting link. Of these, the thermostatic type is the most reliable, provided it is thermally shielded from short local heats due to causes other than fire and is compensated for seasonal temperature changes. However, such thermal shielding, involving special locations, insulations and other precautions has rendered the thermostatic type of re detector less flexible than is desirable for all-purpose use.

Ii accordance with the present invention, a fire detecting device for re alarm systems is provided which responds not only to excessively high temperatures, but also to a predetermined rapid rate of rise of temperature such as is caused by an actual fire, and the response closes a circuit of any suitable type to energize a visible or an audible signal device, or a combination visible and audible signal device.

The invention comprises a pair of cantilever-supported bimetallic thermostatic strips placed in close proximity and so related in thickness and effective length as to deflect at different rates in response to a rapid rise in temperature to close the alarm circuit and to deflect at substantially the same rate in response to a slow rise in temperature up to a maximum degree, whereupon they close the alarm circuit, the transfer of heat to the thermostatic strips being effected by conduction from the casing by a thermal conductor.

In a preferred embodiment of the invention, a thin bimetallic strip of relatively short effective length is supported at one end in parallel relation to a thick bimetallic strip of relatively longer effective length and thermally insulated from the thin strip except for a copper heat conductor leading from the conductive cover rst to the thin thermostatic strip .and then to the thick thermostatic strip. The thermal conductor accordingly conducts heat to the thin or more sensitive strip first in response to a rapid temperature rise to which the cover is exposed, thereby causing the strip to bend toward the thick or less sensitive strip to close electrical contacts carried by the strips and positioned in an alarm circuit. An adjustable stop spaced from the thick or less sensitive strip in the direction of deflection thereof limits its movement in response to a slow temperature rise, during which both strips bend substantially parallel until the thin or sensitive strip eventually engages the stopped thick strip to close the alarm circuit when a predetermined excessively high temperature is reached.

It will be seen that the fire detecting and alarm apparatus of this invention is constructed and arranged to respond only to a predetermined rapid rise in temperature and to an excessively high temperature, but not to slow seasonal rises that are less than the predetermined high degree or to rapid rises of short duration, so that false alarms are precluded. The utilization of the cover as the heat-responsive device and the heat conductor leading therefrom successively to the thermostatic strips enables the detector to be hermetically sealed within the cover against corrosive gases and liquids, hot air blasts of short duration, tampering and contact injury, so that its efficiency remains unimpaired for an indefinitely long period of time.

2,698,368 Patented Dec. 28, 1954 ICC For a more complete understanding of the invention, refernce may be had to the accompanying drawings, in whic Figure 1 is a schematic diagram of a fire alarm system embodying the invention;

Fig. 2 is a longitudinal section through the tire detector of this invention as seen along the line 2 2 of Fig. 3;

Fig. 3 is a transverse section therethrough as seen along the line 33 of Fig. 2; and

Fig. 4 is an enlarged cross-section through the tip of the upper or sensitive strip and shows the electrical contact carried thereby but insulated therefrom.

Referring to Fig. 1 of the drawings, numeral 10 designates the detector of this invention and comprises essentially a thin, relatively short bimetallic thermostat strip 11 having a contact 12 at its free end, and a thick relatively long bimetallic thermostat strip 13 having a contact 14 at its free end and limited in its downward movement by an adjustable stop 15.

Contacts 12 and 14 are adapted to engage upon occurrence of conditions to be described and are connected to the terminals 16 and 17 of the detector 10 in the alarm circuit including a source of power, such as dry cell 18, and a signalling device 19, such as an electric bell, buzzer or horn 19 or an equivalent visual signal like an electric lamp, or both, and adapted to be energized upon engagement of contacts 12 and 14.

The preferred structure of the detector 10 is shown in Figs. 2, 3 and 4 and comprises a suitable base 20 of electrical insulating material, such as a phenolic resin, porcelain, or the like, and adapted to be mounted at any suitable or convenient point where a fire may occur, such as in a warehouse, store, furnace room, or the like.

Sealed to the base 20 by means of a gasket 21 is a nioistureproof cover 22 of a good thermally conductive metal, such as copper or the like, so as to instantly absorb local heat to which it may be exposed.

Clamped on a suitable abutment 23 on the base 20 by means of a rivet 24 are the two bimetallic strips 11 and 13, which may be layers of brass and Invar bonded together, or other combinations of high expanding and lowl expanding metals, and are mounted so that the high expanding layer lies at the top to cause both strips 11 and 14 to bend downwardly when heated. The unmounted lengths of thermostat strips 11 and 13 may be substantially equal as shown in Figs. 1 and 2.

The lower thermostat strip 13 is materially thicker than the upper strip 11, on the order of twice as thick, and is clamped cantilever-fashion between thermal insulating spacer 25 and abutment 23 so as to have the relatively long effective length L2 indicated in Fig. 1. Similarly, the upper or thinner strip 11 is clamped between the relatively long thermal insulating spacers 26 and 27 so as to have an effective length L1 that is materially shorter` than the effective length L2 of the thick strip 13, even though their unmounted lengths are substantially the same.

In order to obtain the same rate of deflection per degree F. for both strips in response to a slow temperature rise, the effective lengths L1 and L2 of the two bimetallic i strips 11 and 13 are predetermined according to the cantilever beam equation wherein D=deflection C=thermal deflection constant for a strip :active length of strip t=thickness of strip T2T1=temperature change in F.

Thus, when the effective lengths L1 and L2 of the strips 11 and 13 are adjusted so that the formulas for each equalize, the normal spacing x between the contacts 12 and 14 remains substantially unchanged fori perature rise is slow, the adjustable stop 15 is so poi 3 sitioned below the lower strip 13 as to stop the movement of the strip 13 after it has dellected the distance y, whereupon the upper strip 11 continues to move toward lower strip 13 until its contact 12 engages contact 14 to energize the alarm 19.

Virtually immediate response of the detector 1t) to a rapid temperature rise is effected by conducting heat directly from the thermally responsive cover 22 to the sensitive thinner thermostatic strip 11 and then to the less sensitive thicker strip 13, by means of the thermal conductor 28. Conductor 28 is a band of a good thermally conductive metal, such as copper, and one end thereof is secured by riveting or soldering to the interior surface of the copper cover 22 and passed between insulating spacer 26 and upper thermostatic strip 11, so as to directly engage the latter for a substantial length as shown in Fig. 2.

The conducting band 28 is then passed between insulating spacer 25 and lower thermostatic strip 13, so as to directly engage the latter, but for a relatively short length. The free end ot' band 28 is anchored to the base 20 by bolt or rivet 17 which also serves as one of the electrical terminals, and the lower section of band 28 from terminal 17 to lower thermostat strip 13 serves as an electrical conductor. Thus, conducting band 28 conducts heat from cover 22 first to the upper thermostatic s'trip 11 andthen to the lower thermostatic strip 13 and a portion thereof also serves as an electrical conductor.

It is desirable that only one therinostatic strip be utilized as an electrical conductor and to that end, the contact 12 carried by the other strip, 11, is insulated therefrom by insulating discs-29 shown in Fig. 4 and is connected by wire 30 to the other terminal 16 mounted on base 20. Accordingly on engagement of contacts 12 and 1-4, the `circuit completed thereby does not traverse upper thermostatic strip 11, but leads from terminal 16, wire 30, Contact 12, contact 14, lower thermostat strip 13, conducting band 2,8 and terminal 17.

In operation of the lire detecting and alarm apparatus of this invention, and assuming that the copper cover 22 is exposed to radiant heat from an adjacent fire, the rapid heat rise is instantly transmitted from cover 2.2 by conductor 28 to thethin sensitive upper thermostatic strip 11 which accordingly responds at once to ternperatures in excess of, say, 135 F. by bending downwardly to engage its contact 12 with the contact 14 of the thick lower thermostat strip 13 which, being less sensitive, has not then responded. The alarm signal is given by the audible signal device 19 or equivalent visual signal, or both.

In the event of a slow rise intemperature such as a seasonal increase during the hot months, the detector is heated uniformly throughout, including both thermostat strips 11y and 13, which accordingly bend in the same direction and at the same rate so that their substantial parallelism is maintained without engagement of contacts 12and 14. This effect is derived by adjustment of the effective lengths L'i and L2 of the thermostat strips 11 and 13 according to the aforementioned equation.

If the slow heat rise continues to, say, 165 F., further deflecting lower thermostat strip 13 is' halted by stop 1S, while upper thermostat strip 11 continues to deec't until its contact 12 engages contact 14 to energize the alarm circuit. The high alarm temperature may be predetermined by adjusting stop 15. ln this way, the iire detector of this invention also responds to fires which are not sufficiently close to heat the cover 22 directly, but by conduction through the atmosphere, floors, walls, and the like.

Although a preferred embodiment of the invention has been illustrated and described herein, it is to be understood that the invention is not limited thereby, but is susceptible of changes in` form and detail within the scope of the appended claims.

We claim:y

l. Iniire alarm apparatus, the combination of a pair of bimetallic thermostatA strips, means including a pair of laminated insulating spacers embracing one of said strips and a pairl of laminated insulating spacers of relatively shorter lengths embracing the other of said strips, thereby defining preestablished effective lengths for each of said strips individually to impart thereto different rates of deflection in responsewto rapid` temperature changes, a thermally conductive enclosure for said strips,

4 a thermal conductor connecting said enclosure with at least one of said strips, and electrical contacts carried by said strips and adapted to energize an alarm circuit upon engagement.

2. In fire alarm apparatus, the combination of a pair of bimetallic thermostat strips having different thicknesses to impart differential` rates of deflection thereto in response to rapid temperature changes, means including a pair of laminated insulating spacers embracing one of said strips and a pair of laminated insulating spacers of relatively shorter lengths embracing the other of said strips, thereby defining preestablished effective lengths for each of said strips individually to impart thereto uniform deliection in response to slow temperature changes, a thermally conductive enclosure for said strips, a thermal conductor connecting said enclosure with the more thermally sensitive strip, and electrical contacts carried by said strips and adapted to energize an alarm circuit upon engagement.

3. ln tire alarm apparatus, the combination of a pair of bimetallic thermostat strips having different thicknesses to impart differential ratesof deflection thereto in response to rapid temperature changes, means including a pair of laminated insulating spacers' embracing one of said strips and a pair of laminated insulating spacers of relatively shorter lengths embracing the other of said strips, thereby defining preestablished effective lengths for each of said strips individually to impart thereto uniform deflection in response to slow temperature changes, a thermally conductive enclosure for said strips, a thermal conductor connecting said enclosure with the more thermally sensitive strip, a stop for stopping the deection of the less thermally sensitive strip in response to a slow temperature rise to a predetermined degree, means for varying the spacing between said stop and the less thermally sensitive strip, and` electrical contacts carried by said strips and adapted to energize an alarm circuit upon enga-gement.

4. In tire alarm apparatus, the combination of a relatively thin bimetallic thermostat strip having a relatively rapid rate of deflection in response to rapid temperature changes, a relatively thick bimetallic thermostat strip having a relatively slow rate of deflection in response to rapid temperature changes, a cantilever support for mounting said strips in` spaced relation, a thermally conductive enclosure for said strips', athermal` conductor serially connecting said enclosure to said strips, said thermal conductor having a` greater area of contact with said thin strip than with said thick strip, and electrical contacts adapted to be engaged by said strips to energize an alarm circuit.

5. In fire alarm apparatus', the combination of a relatively thin bimetallic thermostat strip having a relatively rapid rate of deflection in response to rapid temperature changes, a relatively thick bimetallic thermostat strip having a relatively slow rate of deflection in response to rapid temperature changes, a cantilever support formounting said stripsin spaced relation, a thermally conductive enclosure for said strips, a thermal and electrical conductor serially connecting said enclosure' tosaid thin and thick strips, electrical contacts carried respectively adjacent the free ends of said stripsand adapted to be engaged to energize an alarm circuit, the contact means on one of said strips being electrically connected thereto and the contact means on the other strip being electrically insulated therefrom, said electrical and thermal conductor having an extension portion, terminal means for connecting the apparatus in -an external circuit, said extension portiony being connected toV one of said terminal` means, and, electrical conducting means connecting another terminal means to the 'electrical contactti which is insulatedfrom the strip by which it is'carrie 6. In fire ala'rm apparatus, the combination `of 'first and second bi-rnetallic thermostat strips adapted lto deflect in response to` temperature changes, `a base including an abutment of insulating material for supporting the strips, a cantilever mounting `for the strips for holding the strips in stacked, face to face 'relationship spaced apart in the direction of deflection, said mounting including, for the first strip, 'the said abutment and a first insulating spacer which embrace the first strip at one end, and including, for `the secondstrip, `'afpairof insulating spacers which'e'i'ribrace the secondis'trip-at one 'end Aa`n`cl` which rest on the spacer of the first strip, the saidlpair of spacers being longer than and extending beyond the spacer and abutment of the rst strip, thereby to shorten the deecting length of the second strip, a thermally conductive enclosure for the strips, a thermal and electrical conductor serially connecting the enclosure to the first and second strips, said conductor passing between the second strip and one of said pair of spacers and between the abutment and the first strip, thereby having greater surface contact with the second strip and electrical contact with both strips, a rst electrical terminal 10 connected to the thermal strip, an electrical contact carried by the second strip and electrically insulated therefrom, and a second electrical terminal connected to said contact, whereby contact of the rst and second strips completes an electrical circuit across the terminals and 15 whereby a rapid change in temperature will cause the second strip to deect at a faster rate than the rst.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 578,345 lMaxim Mar. 9, 1897 1,544,549 Barnett July 7, 1925 1,760,470 Bouillon May 27, 1930 2,101,637 Davis Dec. 7, 1937 2,159,090 Kercher May 23, 1939 2,265,684 Campbell Dec. 9, 1941 2,269,863 Shaw Jan. 13, 1942 

